Understanding Your Spectacles’ Prescription

When ordering prescription spectacles or sunglasses on the internet, it is unlikely that you will have face to face contact with your eyewear supplier, therefore it is imperative that the prescription you provide to them is correct.

If the figures are not correct it is highly likely that you will not be able to see properly with the glasses that you will receive.

Should you be unsure of the numbers or signs written on your prescription you should contact the originator to confirm the details before you try to order with any remote supplier.

A prescription is normally written out like this:

R. -2.00/ -1.75 X 155
L. -2.00/ -2.75 X 155

The first figure that you will see on a prescription is the SPHERE power (abbreviated Sph).

This is the main power of the prescription the preceding sign is very important, when it is a minus sign it represents a correction for myopia (short sighted)

e.g. -2.00,

and when it is a positive sign it represent a correction for hypermetropia (longsighted)

e.g. +1.00.

Sometimes the prescription may be written with a DS after the Sphere power

e.g.: +1.00DS.

The “DS” signifies Dioptres Sphere, which is the unit of measurement for spectacle power. More often than not the DS sign is not written.

The next figure you see is the CYLINDER power (abbreviated cyl). This represents the astigmatism in your prescription.

Often this figure is shown like this -1.75cyl.

The astigmatic power is always along a certain angle (axis) from 0 to 180 degrees,

e.g. -1.75 x 175.

Sometimes the sphere and cylinder powers can be separated by a slash.

The R. signifies the right eye. (L. for the left). The right eye is always given first.

e.g.

Rt +2.75 / -3.50 x 125 Lt +3.00 / -2.00 x 55

R. +2.50 / -1.00 x 180
L. +3.25 / -1.25 x 10

This prescription indicates that you are hypermetropic (longsighted), plus have a small amount of astigmatism.

Reading prescription.

If single vision spectacles are required i.e. for distance OR reading only, the prescription will be written as previously mentioned.

Sometimes the prescription will be written with an ADD power after it e.g.:

R +2.50/-1.00 x 55 L +2.00/ -2.00 x 35 ADD +2.50

This is more likely to happen if you are aged 45 or over.

This indicates that you are presbyopic (a diminished ability to focus on objects near to you). This means that you need an additional power to help you read.

You can have presbyopia in addition to any of the prescriptions above, or you may have only presbyopia and perfect distance vision.

In the previous example, to obtain the Reading part of the prescription you add +2.50 to the sphere power

i.e.: R +5.00/ -1.00 x 55 L +4.50/-2.00 x 35

When ordering bifocals or multifocals the distance vision power correction is given with an add power e.g.

R -1.00/-1.25 x 55 ADD +2.00
L -1.50/-1.50 x 165 ADD +2.00

If you wanted just the reading power from the above prescription, if you were ordering single vision reading glasses
again you just add the +2.00 to the Sphere power.

In this example it would be:

R (-1.00 add +2.00 = +1.00) => Rt would read +1.00 / -1.25 x 55
L (-1.50 add +2.00 = +0.50) => Lt would read +0.50 / -1.50 x 165

The complete reading prescription would read:

R +1.00 / -1.25 x 55 L +0.50 / -1.50 x 165.

When ordering prescription spectacles or prescription sunglasses be careful to enter the correct sign.

i.e. +(plus) OR -(minus), also when, ordering bifocals, ensure you include the ‘ADD’ power

IMPORTANT NOTE:

THE PRESCRIPTION FOR CONTACT LENSES IS OFTEN DIFFERENT TO YOUR SPECTACLE PRESCRIPTION